Problem 5.24 particle is traveling in a straight line in a horizontal plane. The mass of the particle is 0.10 kg. The acceleration of the particle is described by the following equation: dv 2 a= = Bt dt where = constant and B = 6 m/s 4. The following additional information is known about the motion of the particle: t t = 0: x = x 0 = 8 m, V= V 0 = 0 and t t = 1 second: V = 30 m/s (a) Determine the time(s) at which the velocity is zero. (b) Determine the total distance traveled when t = 5 sec. (Note that the change in position x is not the same as the distance traveled.) (c) Plot the acceleration, velocity, and position of the particle for 0 t 5 seconds. Determine the time(s) when the motion of the particle changes direction. (d) For the same time interval as in Part (c), plot the linear momentum of the particle, the rate of change of linear momentum of the particle, and the net external force on the particle in the horizontal plane. Determine the time(s) when the net external force changes direction. (e) Discuss how the time(s) you calculated in Part (c) when the particle changed its direction of motion relate to the time(s) you calculated in Part (d) when the net external force changes direction. Is there any relation? Problem 5.25 (dapted from Engineering Mechanics: Statics by Bedford & Fowler, ddison- Wesley) 25 m 25 m 13 m B C 140-kg traffic light is suspended above the street by two cables as shown in the figure above. On a windy day the wind blows from left to right on the figure and creates a horizontal force of 200 N on the traffic light. ssume that the deflection of the traffic light from a vertical orientation due to the crosswind is negligible. (a) Starting with the rate-form of the conservation of linear momentum, use the closed system shown by the dashed lines in the figure to solve for the tension in the cables B and C with and without the crosswind force. (b) How would your analysis change for (a) if your system only included the intersection of the two cables and the traffic light as shown inside the light gray dashed circle? How would you handle the force applied by the hanging traffic light?
Problem 5.26 30-kg package is placed on an incline when a force P is applied to it as shown on the figure. The coefficients of static and kinetic friction between the package and the incline are 0.2 and 0.1, respectively. The motion of the package depends on the magnitude of the force P. (a) Determine the range of values for P for which the package will remain stationary on the inclined plane. (b) ssuming the package is initially stationary, determine its velocity and position 10 seconds after the force P is reduced to zero, i.e. P = 0. φ = 50 o P θ = 20 o Problem 5.27 The mass of Block is 30 kg and the mass of Sphere B is 5 kg. Block slides on the surface and as it slides Sphere B is free to move as shown in the figure. The coefficient of kinetic friction between Block and the surface is 0.24. ssume that the link connecting the Block and the Sphere has negligible mass. (a) Determine the numerical value of the force F, if the angle θ = 20 o is constant. (b) Is the linear momentum of the block increasing, decreasing, or constant? Is the block accelerating, decelerating, or moving at constant velocity? F Sphere θ Block (c) Determine the magnitude and direction of the force of the link acting on the Sphere. Is there tension or compression in the link connecting Block and Sphere B?
Problem 5.28 In a cathode-ray tube, an electron with mass m enters the gap between two charged plates at Point O with a velocity V = V o i. While it is between the charged plates, the electric field generated by the plates subjects the electron to a force F = - e E j where e is the charge of the electron and E is the electric field strength. The plate spacing is 2h, the length of the charged plates is l, and the distance to the screen is L. (See figure below.) ssume that gravitational forces can be neglected and that external forces on the electron are negligible when it is not between the charge plates. (a) Starting with the appropriate conservation and accounting relations, develop an expression for the location of the point of impact of the electron with the screen. Your answer should be presented in terms of the initial speed of the electron (V o ), the mass of the electron (m), the charge of the electron (e), the electric field strength (E), and the dimensions h, l, and L. Clearly identify your system and show how you use the material in the problem and any additional assumptions to develop your answer. (b) Sketch the path of the electron on the figure below. (c) Calculate the actual deflection if the following numerical values are known: V o = 2.2 10 7 m/s; m = 9.11 10-31 kg; e = 1.6 10-19 C (coulombs); E = 15 kn/c L = 100 mm; l = 30 mm; 2h O y - - - - - + + + + l Charged Plates L Screen x Problem 5.29 block with a mass m = 200 kg rests on an inclined plane with an applied load P. Depending upon the magnitude of P, the block may move up the incline, down the incline, or remain stationary. Between the surfaces of contact, the coefficient of static friction is µ s = 0.25 and the coefficient of kinetic friction is µ k = 0.20. Determine the range of the magnitude of the horizontal force P, in newtons, that will keep the block in equilibrium, i.e. not moving. P θ = 60 o
Problem 5.30 The ducted fan unit shown in the figure has mass m = 100 kg and is supported in the vertical position on its flange at. The unit draws in air with a density ρ = 1.200 kg/m 3 and a velocity V 1 = 5 m/s through an inlet with diameter D 1 = 1.00 m. It discharges air through two outlets at the bottom of the fan. The mass flow rate through each outlet is 1/2 of the entering mass flow rate, and the velocity at each outlet is V 2 = V 3 = 15 m/s. Both inlet and outlet pressures are atmospheric. Determine the vertical force R, in newtons, applied to the flange of the fan unit by the supports. D 1 = 1.00 m V 3 = 15 m/s V 1 = 5 m/s Fan Blades V 2 = 15 m/s θ = 55 o θ = 55 o Problem 5.31 crate with mass m = 500 lbm is attached to a motorized winch and positioned on a sloping dock with inclination angle θ = 30 o as shown in the figure. The winch exerts a tensions force T on the crate through the winch cable. The friction coefficients between the crate and the dock surface are µ S = 0.30 for static friction and µ K = 0.25 for kinetic friction. Initially, the crate is stationary and the winch brake is on to prevent any motion. Suddenly at t = 0, the brake is released and the winch exerts a constant tension force T = 100 lbf on the crate. t t > 2 seconds, the tension force exerted by the winch on the crate suddenly increases to a constant value T = 400 lbf (a) Consider the forces on the stationary crate when the winch brake is on and find the value or range of values for the tension force T under these conditions? (b) Consider the crate s motion for 0 t 2 s when the tension force is T = 100 lbf. Find the crate s acceleration, velocity and position at t = 2 seconds. (c) Consider the crate s motion for the period t > 2 s when the tension force is T = 400 lbf. Qualitatively describe how the crate moves during this period (Be concise; use words not numbers!) (d) Calculate the impulse for the tension force T over the time interval t = 0 to 4 seconds. Be sure to indicate both the direction and magnitude. Winch Operating Conditions t < 0 : Winch locked and crate stationary 0 t 2 s : Winch operating; T = 100 lbf. t > 2 s : Winch operating; T = 400 lbf where T is the tension force of the winch on the crate. Winch Winch cable m = 500 lbm µ S = 0.30; µ K = 0.25 θ = 30 o
Problem 5.32 You have been asked to investigate the performance of a jet-propelled boat using a water channel where the water velocity V water can be varied as required. The boat is placed in the channel and tethered so that it is stationary. The boat is jet-propelled by a pump that develops a constant volumetric flow rate of water, V pump. Water enters the aft (front) of the boat through an area of 1 and leaves at the stern (rear) through an area 2. Water flowing over the hull of the boat exerts a drag force on the boat in the direction the water is flowing. This horizontal drag force which includes the net pressure forces on the hull is given by the following equation: F drag = kv where k is a constant. ssume that the angle θ and water density ρ are both known. a) Find expressions for the water velocities V 1 and V 2 in terms of the pump flow rate, V pump. b) Find an expression for the volumetric flow rate through the pump V pump as a function of the water velocity in the channel, V water, when the tension in the tether is zero, i.e. V = f( V ). 2 water pump water Tether θ Pump (2) (1) V water Problem 5.33 10-kg steel sphere is suspended from a 15-kg frame, and the sphere-frame combination slides down a 20 o incline as shown in the figure. The coefficient of kinetic friction between the frame and the incline is µ k = 0.15. 45 o 45 o B Determine the tension in each of the supporting wires, in newtons. 20 o
Problem 5.34 You have been hired by NSCR to analyze vehicle impacts into the wall. For the crash at right, solve for the average reactions (R x,avg and R y,avg ) of the wall on the car in terms of the mass of the vehicle m, the initial velocity V 1, the angle θ, the distances h and d, and the time interval t = t 2 -t 1 assuming the vehicle comes to a complete stop during the time interval. Feel free to assume that the car remains a rectangle during the impact. y x Top View d h θ V 1 Problem 5.35 Blocks and B are identical and each have a mass of 10 kg. Block B is at rest when it is hit by block which is moving with velocity V = 6 m/s just before impact. Blocks and B stick together after the impact, and you may neglect friction during the impact. fter the impact, the velocity of blocks and B decreases due to friction. The coefficient of kinetic friction between all surfaces is µ k = 0.20. (a) Determine the velocity of block and B immediately after hits B. (b) Determine the impulse of the force of block on block B during the impact. (c) Determine the time required for the velocity of the blocks to drop to 1 m/s. (d) Determine the distance traveled by the blocks during this time interval. Before the impact V = 6 m/s fter the impact, blocks and B travel together. B B
Problem 5.36 piece of wood is held at rest on the smooth (frictionless) inclined plane by the stop block at. bullet is traveling as shown in the figure with velocity V when it becomes embedded in the block. The embedding takes a short time, t. The mass of the wood is m w, the mass of the bullet is m B, the angle of the inclined plane is θ and the acceleration due to gravity is g. Provide symbolic solutions to answer the following questions: (a) What is the velocity V a of the bullet/wood immediately after the bullet becomes embedded? SET UP BUT DO NOT SOLVE. Clearly show how you would use your equations to solve for V a For the remaining questions, you may assume that V a is known. (b) What is the average impulsive force acting on the bullet during the impact? (c) What is the equation for the rate of change of velocity of the bullet/wood after the impact? Problem 5.37 Salt water (ρ = 1025 kg/m 3 ) enters a vertical pipe at a volumetric flow rate of 0.5 m 3 /s and is discharged into the atmosphere from the two 30 o outlets as shown in the figure. The flow divides equally between the two outlets. Each of the discharge nozzles has an outlet diameter of 10.0 cm and the inside diameter of the pipe at section - is 25 cm. The pressure of the water at section - is 550 kpa and the atmospheric pressure is 100 kpa. The pipe above the flange and the water within it has a mass of 60 kg. Determine the total force exerted by the lower pipe on the section of pipe above the flange -. Indicate both its magnitude, in newtons, and its direction. 30 O 30 O Salt water flows into the pipe.
Problem 5.38 jet engine with exhaust nozzle is mounted on a test stand as shown in the figure. The engine is mounted as shown on two hangars and a diagonal brace. ll connections are with frictionless pinned joints. Information about the flow area, pressure, and air velocity at three locations along the engine are given in the table. t steady-state operation, air is sucked into the inlet at the rate of 30 kg/s. Determine the direction and the magnitude of the force T in the diagonal brace. Is the brace in tension or compression? 1 m Sec. 1 Sec. 2 Sec. 3 Flow area m 2 0.15 0.16 0.06 1 m 60 o T 60 o Pressure kpa 84 240 114 ir velocity m/s 120 315 600 1 2 3 Problem 5.39 bullet strikes and glances off a flat plate as shown in the figure. The plate is resting on a frictionless horizontal surface. Initially, the bullet has a velocity of 800 ft/s and the plate is stationary. fter striking the plate, the bullet velocity is 600 ft/s. Determine the final velocity of the plate. m Bullet = 0.05 lbm m Plate = 3 lbm 30 o 15 o
Problem 5.40 truck is traveling down a long steady grade (θ = 15 o ) as shown in the figure. The crate has mass m Crate = 500 kg with height H = 1 m and length L = 2 m. The crate rests on the trailer bed and the surface has a static friction coefficient µ S = 0.4 and a kinetic friction coefficient µ K = 0.3. To prevent the load from shifting, the driver must limit his braking. Determine the maximum truck deceleration if the crate does not slide on the trailer bed. m Crate = 500 kg L = 2 m H = 1 m θ = 15 o Problem 5.41 Two blocks rest on an inclined plane with θ = 35 o as shown in the figure. Block has mass m = 13.5 kg and block B has mass m B = 40 kg. The coefficients of static and kinetic friction between all surfaces are µ S = 0.3 and µ k = 0.2, respectively. Initially the blocks are stationary and are supported by a stop block and fixed-length wire, as shown on the figure. When the stop block is removed the block B immediately starts to move because the angle θ is large enough to produce motion. Find the acceleration of block B and the tension in the wire immediately after the stop block is removed. Stop Block θ B Wire
Problem 5.42 The convertible shown is moving at a constant 10 ft/s 45 velocity, v c, in the direction shown. t the instant shown a passenger in the car throws a ball from the car. The magnitude and direction of the initial velocity of the ball with respect to the car, v 0, is shown in the figure. The ball hits the ground 30 ft to the right of the point from which it was released. 4.5 ft v c a) How long does it take the ball to hit the ground from the moment it is released? b) What is the velocity of the car? Problem 5.43 The cart has mass M and is filled with water that has a mass m 0. If a pump ejects water through a nozzle having a cross-sectional area at a constant rate of v 0 relative to the cart, determine the velocity of the cart as a function of time. What is the maximum speed developed by the cart assuming all the water can be pumped out? ssume the frictional resistance to forward motion is F and the density of water is ρ. Problem 5.44 Two swimmers and B, of mass 75 kg and 50 kg, respectively, dive off the end of a 200-kg boat. Each swimmer has a relative horizontal velocity of 3 m/s when leaving the boat. If the boat is initially at rest, determine its final velocity, assuming that (a) the two swimmers dive simultaneously, (b) swimmer dives first, (c) swimmer B dives first. B